273 crankshaft/340

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torred0319

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gotta rebuild my 340 I need a crank is rough non original 318 cast crank now .020 under.
I can get a 273 crank cheap & local. Reading on here crank register is different smaller for older 273 engines i am running a 4 speed will it still be an issue ?
 
i found these weights on here on here
stock 'Cast' Piston Weight Measurements

* 273 (2-Barrel).........530 Grams
* 273 'Commando'......569 Grams
* 318......................592 Grams
* 340......................719 Grams
* 360......................584 Grams

* Speed Pro 'Forged' Replacement Piston for a 340 (723 Grams) this is what i had l2316.030


current 3418645 rods about 754 grams

New set 8 of small block Mopar 6.123" 4340 forged steel SCAT I beam Pro Comp connecting rods. Stock length. 2.124" crank pin (stock), 0.984" pin end (stock). Bushed for full floating. Weight is approx. 595 grams,
 
The others are right: putting stock weight 340 pistons Like the SpeedPro's) will indeed not balance with a 273/318 crank.

My son and I put a '68 273 cast crank in his 340 with SCAT I-beam rods (602 gr IIRC) and KB pistons (595 gr piston and 131 gr pin). That took the bobweight down from 2326 grams for the stock 340 rods/pins/pistons down to 1897 grams for our combo. That is also way under the stock (early) 273/318 bobweight of approximately 2147 grams.

So that 273 crank will balance fine in a 340 with light pistons/pins/rods by taking weight OFF. Our setup balanced up with around 82 grams drilled out of each of the large end counterweights. I just weighed our new parts as a double-check (they were to specification), made the computation and handed the number and the crank to the machinist and told him to balance it to that bobweight. (He was skeptical until I handed him a copy of the spreadsheet LOL.)

So you are on a solid track, OP, assuming your pistons are decently lighter. If you get me your new piston and pin weights, I can get you a close number for your new bobweight in a few minutes.

Get the later 273 cranks with the larger register and you will be fine, or turn it out to the larger diameter. I can't recall the pilot bushing that you may have for options with the smaller register; you might read up on this in the Transmission subforum. Or get a 318 crank.

FWIW, the 273 and 318 bobweights are identical for all years up to at least '74 (and I think beyond '74 but not 100% sure on that); Mopar put in some super heavy pins in the 273 to make up the weight. And the 283's and 318s up to around '74 used a lighter rod at 726 grams.
 
nm9stheham said:
The others are right: putting stock weight 340 pistons Like the SpeedPro's) will indeed not balance with a 273/318 crank.

My son and I put a '68 273 cast crank in his 340 with SCAT I-beam rods (602 gr IIRC) and KB pistons (595 gr piston and 131 gr pin). That took the bobweight down from 2326 grams for the stock 340 rods/pins/pistons down to 1897 grams for our combo. That is also way under the stock (early) 273/318 bobweight of approximately 2147 grams.

So that 273 crank will balance fine in a 340 with light pistons/pins/rods by taking weight OFF. Our setup balanced up with around 82 grams drilled out of each of the large end counterweights. I just weighed our new parts as a double-check (they were to specification), made the computation and handed the number and the crank to the machinist and told him to balance it to that bobweight. (He was skeptical until I handed him a copy of the spreadsheet LOL.)

So you are on a solid track, OP, assuming your pistons are decently lighter. If you get me your new piston and pin weights, I can get you a close number for your new bobweight in a few minutes.

Get the later 273 cranks with the larger register and you will be fine, or turn it out to the larger diameter. I can't recall the pilot bushing that you may have for options with the smaller register; you might read up on this in the Transmission subforum. Or get a 318 crank.

FWIW, the 273 and 318 bobweights are identical for all years up to at least '74 (and I think beyond '74 but not 100% sure on that); Mopar put in some super heavy pins in the 273 to make up the weight. And the 283's and 318s up to around '74 used a lighter rod at 726 grams.
Click to expand...

67 steel crank is what i can get. From what i read it has the smaller register. an auto has to be drilled or turn down the converter. I was wondering if it was the same on 4 speed?? I'm not sure on piston choice there is not really much available for the 340 the block is already 4.070. the cyl walls look bad but measure ok.. I think it will clean up to 4.080 if not 4.100 may be what i have to work with. but i wont know until i have them sonic the block and mag it. My plan was running my x heads but they have large combustion chambers. i need to check them when i get them back from machine shop i'm thinking they were about 74cc. I really didn't even plan on rebuilding it it actually ran ok slow but ok. it smoked a little on start up intake leaked & valve covers leaked it had an old purple cam in it. I planed on reseal upper end and swap in smaller xe268h cam. when i pulled valve springs i noticed couple very loose guides so I pulled the heads sent them to machine shop. oil pan looked kinda dirty so i pulled the short block to clean it throw new set of bearings in and put new gaskets in it that snow balled into the bearings are bad crank needs turned but its already .020. Now im rebuilding the whole thing.... actually thinking now if i got to but crank rods and pistons buy a stroker kit... But how well will a 422 run on factory head or exhaust manifolds.......
 
It will work fine as is with a 4 speed, if the crank has a small register it will need to be opened up for an auto. The crank can be balanced to run factory 340 rods and pistons, and it will live. I have one that has, it spent many years turning 7k rpm as an asphalt circle track engine and lived. In the process of being rebuilt as we speak as a w2 head street 340.



torred0319 said:
67 steel crank is what i can get. From what i read it has the smaller register. an auto has to be drilled or turn down the converter. I was wondering if it was the same on 4 speed?? I'm not sure on piston choice there is not really much available for the 340 the block is already 4.070. the cyl walls look bad but measure ok.. I think it will clean up to 4.080 if not 4.100 may be what i have to work with. but i wont know until i have them sonic the block and mag it. My plan was running my x heads but they have large combustion chambers. i need to check them when i get them back from machine shop i'm thinking they were about 74cc. I really didn't even plan on rebuilding it it actually ran ok slow but ok. it smoked a little on start up intake leaked & valve covers leaked it had an old purple cam in it. I planed on reseal upper end and swap in smaller xe268h cam. when i pulled valve springs i noticed couple very loose guides so I pulled the heads sent them to machine shop. oil pan looked kinda dirty so i pulled the short block to clean it throw new set of bearings in and put new gaskets in it that snow balled into the bearings are bad crank needs turned but its already .020. Now im rebuilding the whole thing.... actually thinking now if i got to but crank rods and pistons buy a stroker kit... But how well will a 422 run on factory head or exhaust manifolds.......
Click to expand...
 
273 is balanced for lighter rods and pistons. When you add the new pistons (+) and lighter rods (-), youll still be way off, needing more weight in the 273 crank throws. Adding weight to a steel crank is $$ tungsten or whatever the balancer down there is going to use. I understand you have no balancers in Mex so Im wondering how the pricepoint of a 273 with a $$ balance and manual trans bushing machining process (?) will compare to a used 340 steel crank sent down there with a cheaper balance that will only have to remove material? Your other option would be to weigh your stuff accurately, and maybe send the specs to Eagle/Scat/? and have them balance you one out of the factory? Tough call with minimal machininsts. you can always balance a cast crank to lighter weight rod specs.
Chrysler/Plymouth/Dodge 340 cast crankshaft | eBay
 
pishta said:
273 is balanced for lighter rods and pistons. When you add the new pistons (+) and lighter rods (-), youll still be way off, needing more weight in the 273 crank throws.
Click to expand...
Not necessarily..... it depends on what rods you use. If you use 602 gram SCAT I-beams with the stock weight 340 pistons (like SpeedPro's), the bobweight drops to down around 2059 grams, which is lighter than the stock 273/318 bobweight (at around 2147 grams). So in that case, you can balance a 273/318 crank for a 340 by simply taking weight off the 273/318 crank.

It cost me under $100 to have our 273 crank rebalanced to light 340 pistons/pins/rods. It was cheap because I gave the bobweight to the machinst; he did not measure it; processing the rods and pistons is where most of the balance cost is.

pishta said:
Adding weight to a steel crank is $$ tungsten or whatever the balancer down there is going to use. I understand you have no balancers in Mex so Im wondering how the pricepoint of a 273 with a $$ balance and manual trans bushing machining process (?) will compare to a used 340 steel crank sent down there with a cheaper balance that will only have to remove material? Your other option would be to weigh your stuff accurately, and maybe send the specs to Eagle/Scat/? and have them balance you one out of the factory? Tough call with minimal machininsts. you can always balance a cast crank to lighter weight rod specs.
Chrysler/Plymouth/Dodge 340 cast crankshaft | eBay
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Yeah, you can do anything, but adding weight is pricey.

Are you saying there are no shops in Mexico that can balance a crankshaft? I am surprised....

OP, I'd suggest that you to look at SRP or KB pistons, like the KB243's. With the open heads, they will be above-deck like the stock or SpeedPro 340 pistons, and your compression will be right around stock. Really light too. So you can save a LOT of $$ versus a stroker kit. Hope you block works out.
 
dibbons, I thought it was you! Torred0319 diregard Mexico reference. I was confused who started this post. Balance away!
 
nm9stheham said:
The others are right: putting stock weight 340 pistons Like the SpeedPro's) will indeed not balance with a 273/318 crank.

My son and I put a '68 273 cast crank in his 340 with SCAT I-beam rods (602 gr IIRC) and KB pistons (595 gr piston and 131 gr pin). That took the bobweight down from 2326 grams for the stock 340 rods/pins/pistons down to 1897 grams for our combo. That is also way under the stock (early) 273/318 bobweight of approximately 2147 grams.

So that 273 crank will balance fine in a 340 with light pistons/pins/rods by taking weight OFF. Our setup balanced up with around 82 grams drilled out of each of the large end counterweights. I just weighed our new parts as a double-check (they were to specification), made the computation and handed the number and the crank to the machinist and told him to balance it to that bobweight. (He was skeptical until I handed him a copy of the spreadsheet LOL.)

So you are on a solid track, OP, assuming your pistons are decently lighter. If you get me your new piston and pin weights, I can get you a close number for your new bobweight in a few minutes.

Get the later 273 cranks with the larger register and you will be fine, or turn it out to the larger diameter. I can't recall the pilot bushing that you may have for options with the smaller register; you might read up on this in the Transmission subforum. Or get a 318 crank.

FWIW, the 273 and 318 bobweights are identical for all years up to at least '74 (and I think beyond '74 but not 100% sure on that); Mopar put in some super heavy pins in the 273 to make up the weight. And the 283's and 318s up to around '74 used a lighter rod at 726 grams.
Click to expand...
Where can you buy 131g piston pins? Thanks, Guttorm Frisell
 
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